But extracting either from seawater does not really make any sense. Some mid-east countries desalinate so they can pursue idiotic schemes to grow wheat in the desert, when they could just buy wheat for far less. California has a few desalination plants, because of dumb policies that vastly inflate the cost of water to urban consumers, while subsiding the delivery of rainwater to farmers growing rice and cotton in the desert.
Forget rice and cotton. We'd be happy if they'd stop growing alfalfa and almonds in the desert.... With that said, even if we got rid of that problem, eventually California's growing population would still require desalination. The drought simply moves that date closer in many places.